When we started out in the SUV for Tikal on my first day in Guatemala's Petén jungle, my guide, Arturo Godoy, stopped at a roadside store and bought three two-liter bottles of water. Are you kidding? I thought. This was the dry run as far as Maya ruins go. Paved road all the way, clearings around all the pyramids, well-marked trails, cafeteria.

Forget it. Tikal was gorgeous and well tended, but there were no cafeterias, no food, no water, and no guidance. Temperature and humidity hovered in the mid-90s (32ºC) under bright sunshine. There was a parking lot, but forget the tour buses. You want to see Tikal, you walk. Within 20 minutes, I was soaked in sweat to the knees. Ten minutes later, I was wondering why I was carrying reference books and folders in my backpack.

I was exhausted after about an hour, but I had at least four more days to go. How was I going to survive? Here's what I discovered: First, empty the day pack of everything, except for the sandwich, trail mix, and water. And don't forget to eat. Second, let Arturo—he's about 30, and I'm not—carry two bottles of water, and you carry one. Third, drink your water first, and don't forget to share.

Thankfully, it got easier. At Tikal, I walked for two hours; at Dos Pilas, I walked for nearly five hours; and at Waka, I was able to do more than seven hours and enjoy a couple of beers afterward. I felt pretty proud of myself.

What was the trickiest part of the assignmet?

Cutting trees in Guatemala's national jungle preserves is illegal, but that doesn't stop it from happening. Mahogany (when it can be found), cedar, and hormigo (for musical instruments) are all fair game. On the way to the Maya ruins at Dos Pilas, we turned off the highway at a town called Las Pozas, noticing nothing there except about 20 mom-and-pop sawmills. We soon saw why.

Dos Pilas was supposed to be easy to find, but the dirt track to the ruins kept forking in the woods. Each false fork dead-ended in a clearing, and each clearing had a sawed-off tree stump. We parked the SUV when we could go no farther and continued on foot, following blind alleys and doubling back. Finally we came to a clearing that wasn't empty. Instead, there was a fresh cedar tree lying across a pair of makeshift sawhorses. The trunk had been cut lengthwise, and a chainsaw sat on a nearby stump.

"Well," Arturo whispered. "I think it's time to go." He turned around and I followed, thinking about what it would be like to be caught in the middle of nowhere by a couple of poachers with a chainsaw. We never saw them, but I still wonder where they were and why they didn't hear us.

Did you come across anything particularly interesting?

There's really nothing quite like the Petén jungle. When people think about Maya ruins, they think of Tikal, or other beautiful, shining cities carved from the wilderness. Oddly enough, though, during the Maya heyday, around A.D. 600, millions of people lived in the Petén—so many that there probably wasn't a jungle at all. Back then, today's hidden shrines were simply the big towns in a settled countryside. It was only after they were abandoned—around A.D. 1000—that the jungle converted the Maya heartland into an enchanted forest.

Exploring the jungle, I soon found out that there's a big difference today between a "restored" site, like Tikal or Copán, and a "discovered," "surveyed," or "excavated" site, like Waka or Dos Pilas. Most ruins are unrecognizable to the untrained eye. On the way to Waka in the north central Petén, I hiked for three hours over forest-covered hills, which, as Arturo explained, were probably temple mounds or other ceremonial buildings, cloaked with a millennium's-worth of vines and creepers. And the "site" was more of the same: tree-covered dirt, with a bit scraped away in places to reveal the beginnings of a stairway or an inscription. Archaeologists can draw the outlines of these cities by looking at a few outcrops. But all I could see were hills, filled with howler monkeys screaming at me from the trees.